Amongst this amazing result I must ask why the FPU would slow down the design?

I explained that in Post#33 - it's a very technical explanation. In layman's terms, imagine a room with just a few people: Noise level is low, and communication is easy. Then imagine a room with lots of people, where you always have a basic noise level. If a speaker wants to reach a person at the far end of the room, he has more problems to do that compared to the room with just a few persons. Essentially, the FPU would act like the "too many persons" on the data bus.